A compound represented by the formula (I) is known to be useful as an antioxidant of a thermoplastic resin such as polyolefin from patent Publication 1, and a process for producing a thermoplastic resin composition by simultaneously blending calcium stearate which is one kind of neutralizing agents, a thermoplastic resin, and a compound (1), and melting-kneading them is specifically disclosed in patent Publication 1.

In the formula, two R's, two R2s, R4 and R5 each represent independently a hydrogen atom, an alkyl group having a carbon number of 1 to 8, a cycloalkyl group having a carbon number of 5 to 8, an alkylcycloalkyl group having a carbon number of 6 to 12, an aralkyl group having a carbon number of 7 to 12, or a phenyl group, two R3s each represent independently a hydrogen atom, or an alkyl group having a carbon number of 1 to 8, X represents a single bond, a sulfur atom or a —CHR6— group, wherein R6 represents a hydrogen atom, an alkyl group having a carbon number of 1 to 8, or a cycloalkyl group having a carbon number of 5 to 8,
A represents an alkylene group having a carbon number of 2 to 8, or a *—COR7— group, wherein R7 represents a single bond, or an alkylene group having a carbon number of 1 to 8, and a symbol * represents a bond with an oxygen atom of a >P—O— portion,
one of Y and Z represents a hydroxyl group, an alkoxy group having a carbon number of 1 to 8, or an aralkyloxy group having a carbon number of 7 to 12, and the other of Y and Z represents a hydrogen atom, or an alkyl group having a carbon number of 1 to 8,
provided that, when Y is a hydroxyl group, one of R4 and R5 represents an alkyl group having a carbon number of 3 to 8, a cycloalkyl group having a carbon number of 5 to 8, an alkylcycloalkyl group having a carbon number of 6 to 12, an aralkyl group having a carbon number of 7 to 12, or a phenyl group.
[Patent Publication 1] JP-A No. 10-273494 (Claims, Example 14)